Methods for making unmodified polyvinyl alcohol films

ABSTRACT

This invention relates, in general, to blend compositions of an unmodified poly vinyl alcohol and a thermoplastic elastomer and thermoplastic film and fiber structures comprising these blend compositions. More specifically, this invention relates to substantially water-free films and fibers comprising unmodified polyvinyl alcohol and a thermoplastic elastomer.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/464,625, filed Dec. 16, 1999, which is adivision of U.S. patent application Ser. No. 09/088,352, filed Jun. 1,1998, now U.S. Pat. No. 6,020,425.

FIELD OF THE INVENTION

[0002] This invention relates, in general, to blend compositions of anunmodified poly vinyl alcohol and a thermoplastic elastomer andthermoplastic film and fiber structures comprising these blendcompositions. More specifically, this invention relates to substantiallywater-free films and fibers comprising unmodified polyvinyl alcohol anda thermoplastic elastomer.

BACKGROUND OF THE INVENTION

[0003] Personal care articles are widely used in today's society. Manyof these articles use films and fibers that are thermoplastic.Additionally, these articles use films and fibers that have differentproperties, depending on their location in the product. For example,some films and fibers are elastomeric. Others are breathable while stillothers act as liquid barriers. Finally, some of the films and fibers,especially those in contact with the wearer of the product, are designedto be softer to the touch. These different films typically comprisepolymers or polymer blends that, when processed, form a film or fiberhaving the desired characteristic or characteristics.

[0004] Additionally, in an attempt to deal with decreasing land-fill andsolid waste disposal many of these films and fibers are designed to bewater-dispersible such that the product will partially or completelydisperse in water, thereby allowing the product to be disposed ofwithout dumping or incineration. These products may be placed in sewagesystems or may be flushed down a conventional toilet. To produce thesewater-dispersible products, the films and fibers used in the productswill typically use blend compositions that include a water-dispersiblepolymer such as polyethylene oxide or polyvinyl alcohol.

[0005] Polyvinyl alcohol (PVOH) is a commodity polymer that is used in awide variety of different applications. Many of these applications arethermoplastic. However, PVOH is generally regarded as anon-thermoplastic polymer. PVOH has a high melting point of about 200°C. depending on the degree of hydrolysis. Accordingly, as PVOH is heatednear its melting point, yellowing and discoloration occur. Therefore,when using PVOH as a base material for thermoplastic applications, thePVOH must usually be modified.

[0006] Modified PVOH is used in many different water-dispersiblethermoformable articles, such as fibers, films and fabrics whichmaintain their integrity and strength when in use, but dissolve anddisperse when placed in contact with water. Unmodified PVOH is used inindustry for many different solution-based applications and is notgenerally considered to be thermoformable or melt-processable. Some suchapplications for unmodified PVOH include warp sizing in textiles, fabricfinishing, adhesives, paper processing additives, andemulsifiers/dispersants.

[0007] The prior art has demonstrated some success in modifying PVOH foruse in thermoplastic applications. By “modified” PVOH, it is meant PVOHresin which has been chemically modified, including PVOH having anothercompound grafted thereto, or PVOH resin that has been mixed with one ormore plasticizers. In each instance, these “modifications” have beenneeded to permit PVOH to be used in thermoformable articles.

[0008] To overcome the thermoplastic processing problems, chemicallymodified PVOH has been used. Some prior art teachings have used ethersof PVOH, ethoxylated PVOH or lacton-modified PVOH to producethermoformable articles.

[0009] The prior art has also used PVOH that has not been modifiedstructurally by adding a plasticizing agent to the PVOH which permitsthe PVOH to be extruded into films and fibers. Examples of plasticizersinclude water, ethylene glycol, glycerin and ethanolamine.

[0010] However, there are problems associated with the addition ofplasticizers to PVOH. One of the most pronounced problems duringprocessing is the fogging of the volatile plasticizer during the meltextrusion and condensing of vapor and effects of the vapor to theoperating environment. In addition, the extruded articles such as filmsor fibers lose the plasticizers since the plasticizer molecules diffuseout of the film or fibers. This causes the films or fibers to becomebrittle over time and often causes the article to fail.

[0011] Additionally, films and fibers including modified PVOH or PVOHand a plasticizer may be limited in their utility. These films andfibers may be too stiff to be used for certain applications.Additionally, the texture of the films may not be soft enough forcomfortable contact with the skin of an individual. Finally, these filmsand fibers may be too “noisy” such that bending or flexing of the filmor fiber causes an audible sound that may be distracting to the user ofthe product.

[0012] Accordingly, what is needed is an unmodified PVOH that may beused in blend compositions that are thermoplastically formed into filmsand fibers. These films and fibers may then be used in the production ofwater-dispersible, flushable articles without the use of plasticizingagents. These fibers, films and fabrics could be used in products suchas personal care products, diapers, feminine napkins and pads, trainingpants, wipes, adult incontinence products, release liners, productpackaging, etc., which contain the above-mentioned fibers, films andfabrics. Additionally, what is needed are thermoplastically formed filmsand fibers that have enhanced softness and ductility and produce lessnoise when bent or flexed.

SUMMARY OF THE INVENTION

[0013] Accordingly, the present invention desires to produce films andfibers including blend compositions having unmodified PVOH and athermoplastic elastomer.

[0014] Another desire of the present invention is to use unmodified PVOHand a thermoplastic elastomer in films and fibers without the use of aplasticizing agent.

[0015] These and other desires are satisfied by the present invention.The present invention discloses the selection and use ofcommercially-available grades of PVOH for thermoplastic applications.“Thermoplastic” is defined, herein, as a resin which can be melted andeasily extruded to form a desired article, i.e., the material is meltprocessable. These commercially-available grades of PVOH are combinedwith a thermoplastic elastomer to provide a blend composition useful inthe production of films and fibers that have enhanced softness andductility and produce less noise.

[0016] PVOH is a commodity polymer, commonly used in solution-basedapplications. Since it is a commodity polymer, thermoplastic articlesmade using unmodified PVOH are generally less expensive than articlesmade using modified PVOH due to the additional process steps required tomodify the PVOH. Also, unmodified PVOH is, in general, less expensivethan other water-soluble polymers.

[0017] In its unmodified form, PVOH has not been used for thermoplasticapplications. Typically, some modification of the PVOH, such as chemicalgrafting or addition of plasticizer, is necessary to achieve meltprocessability for PVOH. In the present invention, a window ofthermoplastic processability has been discovered and defined forunmodified, commercially-available PVOH, according to: 1) thecomposition or % hydrolysis of the PVOH, 2) the molecular weight of thePVOH, 3) the solution viscosity of the PVOH, or 4) the melt viscosity ofthe PVOH. The selected grades of PVOH have demonstratedthermoplasticity, allowing for continuous, melt extrusion or conversioninto thin films in a continuous, extrusion process.

[0018] These grades of PVOH are also useful for melt spinning of fibers,injection molding or other thermoplastic applications. Extruded films ofthe unmodified PVOH/thermoplastic elastomer blends described herein havevery high strength and modulus, excellent clarity, and fastcrystallization and solidification rates. The advantages of meltprocessing a thermoplastic, unmodified PVOH into a useful, strong,clear, water-soluble article are evident. Melt processing is a desirablethermoforming process compared to solution processing. Melt processingeliminates the need to add steps such as chemical grafting, addition ofa plasticizer, or other modification in order to achieve meltprocessability.

[0019] These grades of PVOH may be mixed with additional polymers, suchas thermoplastic elastomers, to provide desired characteristics to thefilms and fibers, such as enhanced ductility, enhanced softness andlower noise generation.

DETAILED DESCRIPTION

[0020] PVOH is generally produced by a two step process as shown inScheme 1. Since vinyl alcohol is not a stable monomer, thepolymerization of vinyl alcohol is not an option for making PVOH.Instead, the process utilizes a readily available monomer, vinylacetate, as the starting point. The first step is the polymerization ofvinyl acetate into polyvinyl acetate (PVA). The second step is thehydrolysis or alcoholysis of PVA into a copolymer of vinyl acetate andvinyl alcohol, or polyvinyl alcohol (PVOH). Depending on the hydrolysislevel as defined in the equation in Scheme 1, a wide range of PVOHcopolymers can be produced when the hydrolysis reaction is allowed toreach certain conversion levels.

[0021] For PVOH, the degree of hydrolysis is controlled during thealcoholysis reaction and is independent of the control of the molecularweight of the PVOH formed. Fully hydrolyzed PVOH is obtained ifalcoholysis is allowed to go to completion. The reaction is terminatedby removing or neutralizing the sodium hydroxide catalyst used in theprocess. Typically, a small amount of water is added to the reactionvessel to promote the saponification reaction of PVA. The extent ofhydrolysis is inversely proportional to the amount of water added. Thealcoholysis can be carried out in a highly agitated slurry reactor. Afine precipitate forms as PVA, which is then converted to PVOH. The PVOHproduct is then washed with methanol and is filtered and dried to form awhite, granular powder.

[0022] The molecular weight of the PVOH is controlled by thepolymerization condition of vinyl acetate. Many properties of PVOHdepend on the degree of hydrolysis and the molecular weight. As themolecular weight increases, the solution viscosity, tensile strength,water resistance, adhesive strength, and solvent resistance increase. Asmolecular weight decreases, the flexibility, water solubility, and easeof solvation increase. As the degree of hydrolysis increases, the waterresistance, tensile strength, block resistance, solvent resistance, andadhesion to polar substrates increase. As the degree of hydrolysisdecreases, the water solubility, flexibility, water sensitivity andadhesion to hydrophobic substrates increase.

[0023] Due to the strong dependence of PVOH on the molecular weight anddegree of hydrolysis, PVOH is typically supplied in combination of thesetwo parameters. PVOH is classified into 1) partially hydrolyzed (87.0 to89.0% hydrolysis); 2) intermediately hydrolyzed (95.5 to 96.5%hydrolysis); 3) fully hydrolyzed (98.0 to 98.8% hydrolysis); and 4)super hydrolyzed (>99.3% hydrolysis). Within each category of PVOH, theresin is differentiated by solution viscosity, measured at 4% solutionin water at 20° C. in centipoise. The viscosity is used as a molecularweight measure since solution viscosity is typically related to themolecular weight by the well known Mark-Houwink equation:

η=KM _(v) ^(a)

[0024] wherein

[0025] η=intrinsic viscosity

[0026] K=constant (dependent upon the polymer)

[0027] M_(v)=molecular weight

[0028] a=factor based on the rigidity of the polymer chains and isdependent on the polymer.

[0029] For unmodified PVOH, it was known that higher molecular weightgrades were not thermoplastic. It was surprising that unmodified PVOH atlower molecular weights would be thermoplastic based on the non-meltprocessability of higher molecular weights grades. Unmodified PVOH withweight average molecular weight as low as 8750 g/mole was discovered tobe thermoplastic and melt processable, with high melt strength,excellent film strength and great clarity. Typically, a polymer withsuch a low starting molecular weight would not be expected to be meltprocessable into a useful material.

[0030] Additionally, it was discovered that the melt viscosity of thePVOH grades could be used to determine which grades of PVOH werethermoplastic. In general, those grades having a melt viscosity lessthan about 1500 Pa·s at a shear rate of 500 s⁻¹ were determined to bemelt processable.

[0031] Not all grades of PVOH were discovered to be thermoplastic. ThePVOH grades useful in this invention desirably have a solution viscosityof less than about 10 cp in a 4% water solution at 20° C. and ahydrolysis of less than about 90%. Examples of commercially-availablegrades of PVOH useful in this invention are ELVANOL® 51-05 from DuPont(Wilmington, Del.), AIRVOL® 203 and 205 from Air Products and Chemical,Inc. (Allentown, Pa.), and GOHSENOL® KP-06 from Nippon Gohsei (Japan).PVOH is typically sold in powder or granule form, however pellets orother forms of resin can be used in this invention since the physicalform of PVOH does not affect melt processability.

[0032] Additionally, depending on the type of blend application forwhich the PVOH will be used, films or fibers, the exact processingcharacteristics may vary. For example, some of the thermoplastic gradesmay be better suited for the production of thermoplastic films whileother grades may be more useful for the production of fibers. The exactgrade to use will depend upon the item being made and the elastomer thatis blended with the PVOH.

[0033] The present invention uses these thermoplastic PVOH grades withan additional compound to form blend compositions. These blendcompositions may then be formed into thermoplastic articles such asfilms and fiber. The additional compound is used to enhance theproperties of the resulting films and fibers. In the present invention,a thermoplastic elastomer is used to help produce films that are softer,more ductile and less noisy than films comprising PVOH alone.

[0034] The blends including thermoplastic PVOH grades and athermoplastic elastomer may be extruded using most known extrudingdevices. In general, while a thermoplastic film may be extruded atextrusion temperatures above the melting point of the PVOH/elastomerblend, it is preferred to use extrusion temperatures near the meltingpoint as the resulting films and fibers are generally clearer, havefewer imperfections, are more ductile and stronger, and can be drawninto much thinner films.

[0035] As discussed earlier, the films and fibers of the presentinvention can be extruded from unmodified PVOH/elastomer blends withoutthe use of a plasticizer. Many different plasticizers are known,including, for example, ethylene glycol, glycerines and ethanolamine. Inaddition to these plasticizers, water is also known to be used as aplasticizer in the production of PVOH films and fibers. However, theseplasticizers, including water, have several disadvantages when used inthe production of films and fibers. In general, plasticizers, includingwater, will slowly diffuse out of a PVOH film or fiber causing the filmor fiber to become lucid and brittle and therefore more likely to breakor shatter.

[0036] Additionally, plasticizers, including water, added to PVOH maycause bubbling of the film during the extrusion process. This isespecially true with water. Therefore, care must be taken prior to theblending with an elastomer and production of the film to ensure that thePVOH powder or pellets remain substantially water-free. This helps toensure that the films and fibers produced are also substantiallywater-free. By “substantially water-free” it is meant that the films andfibers produced using the unmodified PVOH/elastomer blends contain lessthan about 2.0 percent by weight of water. Desirably, the films andfibers contain less than about 1.0 percent by weight of water. Moredesirably, the films and fibers contain less than 0.5 percent by weightof water.

[0037] There are three basic types of thermoplastic elastomers: 1)styrenic thermoplastic elastomers, 2) hard/polymer elastomercombinations, and 3) multi-block polymers with crystalline hardsegments.

[0038] For styrenic thermoplastic elastomers, the elastomer may be anA-B-A block polymer where “A” is a polystyrene and “B” is an elastomersegment. The elastomeric segments may be selected from polybutadiene,polyisoprene, poly(ethylene-butylene), and poly(ethylene-propylene).Accordingly, these polymers may be referred to as S-B-S, S-I-S, S-EB-S,and S-EP-S, respectively, where “S” refers to polystyrene, “B” refers topolybutadiene, “I” refers to polyisoprene, “EB” refers to poly(ethylene-butylene), and “EP” refers to poly (ethylene-propylene).

[0039] Hard/polymer elastomer combinations include a hard thermoplasticpolymer, such as polypropylene, in a fine dispersion within a matrix ofan elastomer. The elastomer may be selected fromethylene-propylene-diene monomer (EPDM) or ethylene-propylene copolymer(EPR). Other elastomers that may be used include nitrile, butyl, andnatural rubbers.

[0040] Multi-block polymers with crystalline hard segments generallyinclude multi-block (A-B)_(n) structures, wherein “A” is a crystallinethermoplastic, while “B” is a softer, elastomeric segment that isamorphous. Examples of hard segments include, but are not limited to,thermoplastic polyurethanes, thermoplastic polyesters, and thermoplasticpolyamides. Examples of soft segments include, but are not limited to,polyesters.

[0041] The importance of this invention is that PVOH/elastomer blendshave been discovered that may be directly extruded into a water-soluble,thin film without the need for any chemical modification of the PVOH orthe addition of a plasticizer. The elimination of any chemicalmodification of the PVOH eliminates the labor intensive step ofchemically modifying or grafting the PVOH. The elimination of aplasticizer admixed with the PVOH relieves the common problems involvedwith plasticizers as previously discussed. The water-soluble film of thepresent invention will keep its original properties and in-useperformance unlike a PVOH/elastomer film containing a plasticizer whichwill become brittle over time.

[0042] One additional advantage in the production of water-solubleproducts from the PVOH/elastomer films and fibers of the presentinvention is in the product converting stage. PVOH has a higher meltingpoint than many other water-soluble polymer systems used for makingwater-dispersible, flushable articles, including, for example,polyethylene oxide-based materials. PVOH film can withstand heat from ahot-applied melt adhesive which may be used during product construction.In contrast, PEO-based materials have limitations in this aspect due tothe low melting temperature of the PEO of about 60 to 70° C. Therefore,the PVOH/elastomer films and fibers of the present invention have greatusefulness in the production of water-dispersible, flushable products.

[0043] The PVOH/elastomer blends, films and fibers of the presentinvention include a thermoplastic elastomer that enhances certaincharacteristics of the films and fibers when compared to films andfibers comprising only unmodified PVOH. The elastomer imparts improvedsoftness and ductility to the film while reducing the amount of noisethe film makes when manipulated. These features are very useful forfilms that are used in a personal care article, such as a diaper,feminine article, incontinence device, among others.

[0044] The present invention uses a thermoplastic elastomer. Suitablethermoplastic elastomers include, but are not limited to, KRATON®polymers from Shell, such as Kraton D, a S-B-S or S-I-S polymer, andKraton G, a S-EB-S or S-EP-S polymer, elastomeric polyurethanes,ethylene-octene copolymers, polyester polyurethane, natural rubber,nitrile rubber, butyl rubber, ethylene-propylene terpolymers, siliconerubber, polyurethane rubber, thermoplastic rubbers, elastomeric blockcopolymers, copolymers of polyethylene oxide and polybutyleneterephthalate, polyamide-polyether block copolymers, styrenic blockcopolymers, elastomeric polypropylene, or mixtures thereof. The amountof thermoplastic elastomer that may be used is in the amount of fromabout 1 to about 99% by weight of the PVOH/elastomer blend. Desirably,the blend comprises from about 50 to about 90% by weight PVOH and fromabout 50 to about 10% thermoplastic elastomer. Even more desirably, theblend comprises from about 65 to about 80% by weight PVOH and from about35 to about 20% thermoplastic elastomer.

[0045] The relative amounts of PVOH to that of thermoplastic elastomersdetermine the water-responsiveness of the resulting PVOH/thermoplasticelastomer films. When the PVOH is a volumetric majority component, theresulting article is water-dispersible or water-disintegratable asdefined by standard test methods. As used herein, the term“water-responsive” includes articles that are water-dispersible,water-disintegratable and water-weakened. “Water-dispersible” is usedherein to describe a 5 mil (0.005 of an inch) film that, under thewater-responsiveness test described below, dissolves or breaks intopieces smaller than a 20 mesh screen.

[0046] “Water-disintegratable” describes a 5 mil film that, under thewater-responsiveness test, breaks into multiple pieces after two minuteswith some of the pieces caught by a 20 mesh screen. “Water-weakened”describes a 5 mil film that, under the water-responsiveness test,remains intact, but loses rigidity and becomes drapable, i.e., will bendwith an external force applied to the film when it is held by one cornerat a substantially horizontal position.

[0047] The present invention is further illustrated by the followingexamples, which are not to be construed in any way as imposinglimitations upon the scope thereof. On the contrary, it is to be clearlyunderstood that resort may be had to various other embodiments,modifications, and equivalents thereof which, after reading thedescription herein, may suggest themselves to those skilled in the artwithout departing from the spirit of the present invention and/or thescope of the appended claims.

EXAMPLES Example 1

[0048] The melt processability of PVOH was first demonstrated by atwin-screw extrusion process. A Haake (Paramus, N.J.) TW-100counter-rotating twin-screw extruder, fitted with a 4″ cast film die wasused. The extruder had a length of 300 mm. Each conical screw had adiameter of 30 mm at the feed port and a diameter of 20 mm at the die. Agrade of relatively low degree hydrolysis from Nippon Gohsei, GOSHENOL®KP-06, was selected. This PVOH resin was manufactured for use as adispersion agent for use in aqueous solution applications. It was notintended for melt processing. The degree of hydrolysis is 71-74%, it'sviscosity in a 4% solution in water at 20° C. is 5 to 7 cp, as measuredby Hoeppler falling ball method. It is supplied as a white granulatepowder. To test the possibility for thermoplastic process, the resin wasfed to the Haake twin-screw extruder directly without pelletization.

[0049] An extruded film was collected by a chilled wind-up roll.Initially, the screw speed was set at 134 rpm. The barrel temperatureswere 150, 185, 185 and 190° C. for zones 1, 2, 3 and 4 (die)respectively. Due to intensive shear heating, the melt temperature wasraised above the set temperature of the film die, reaching about 225° C.Under these conditions, it was surprising that a thick film of about 4-6mil could be produced from this resin which is supposed to benon-thermoplastic. However, the quality of the film was poor and therewere many holes in the film. The films were relatively hazy and not asclear at typical PVOH films. The film was extremely rigid and brittle.On the film there were many deep flow lines visually observable. Themelt strength of PVOH under these conditions was weak. The PVOH filmmade under this temperature was discolored and appeared slightlyyellowish.

Example 2

[0050] In Example 2, the same PVOH resin used in Example 1 was tested todetermine whether the film processing conditions could be improved.First, the extrusion temperature profile was modified. The barreltemperatures were set at 150, 185, 185 and 180° C. for zones 1, 2, 3 and4 (die) respectively. The screw speed was maintained at 134 rpm. Thislower die set temperature brought down the melt temperature to about 195to 200° C. Surprisingly, as the melt temperature of the PVOH dropped,the film properties improved dramatically. At a melt temperature ofabout 195 to 200° C., the melt strength of PVOH improved greatly suchthat a PVOH film could be drawn down to less than 0.2 mil. In contrastto the hazy appearance of the PVOH made in Example 1, the PVOH film madein this example under the lower melt temperature had excellent clarityand was essentially free of film defects.

[0051] Compared to the PVOH film in Example 1, the film made at a lowertemperature had greater strength and softness. The tensile properties ofthe pellet-derived PVOH film were tested on a Sintech 1/D tensile testeravailable from MTS Systems Corp. (Machesny Park, Ill.). The PVOH filmhad a high melt strength such that the winding up of the film at highspeed did not cause any tearing or breaking of the PVOH film. The peakstress of the film was over 60 MPa. The elongation-at-break of the PVOHwas about 73%. The modulus of the film was also high, slightly over 1800MPa.

Example 3

[0052] The same PVOH resin used in Example 1 was used for this example.PVOH is usually delivered from the manufacture in a powdered form. Sincepolymers in the pellet form are generally easier to work with, anexperiment was devised to see if cast films created directly from PVOHpowder had different tensile properties that those created from PVOH inthe pellet form. PVOH pellets were made by extruding PVOH powder on aWerner & Pfleiderer (Ramsey, N.J.) ZSK-30 extruder at 20 lb/hr and 300rpm. The ZSK-30 extruder has a pair of co-rotating screws arranged inparallel with the center-to-center distance between the shafts of thetwo screws at 26.2 mm. The nominal screw diameters are 30 mm. The actualouter diameters of the screws are 30 mm and the inner screw diametersare 21.3 mm. The thread depths are 4.7 mm. The length of the screws are1328 mm and the total processing section length was 1338 mm. This ZSK-30extruder had 14 processing barrels which were numbered consecutively 1to 14 from the feed barrel to the die. The first barrel was not heated,but cooled by water. Barrels 2 to 14 were divided into 7 zones. Barrels2 and 3 comprised zone 1. Barrels 4 and 5 comprised zone 2. Barrels 6and 7 comprised zone 3. Barrels 8 and 9 comprised zone 4. Barrels 10 and11 comprised zone 5. Barrels 12 and 13 comprised zone 6. Barrel 14 (die)comprised zone 14. The extruded melt strands were cooled by air on a 15foot conveyer belt equipped with fans, and then pelletized. As a rule ofthumb, it was expected that the films from pellets would have lowertensile strength than the powder-derived films since the PVOH resinsuffers from additional thermomechanical degradation during the extrapass through the extruder.

[0053] However, the PVOH pellets made on the ZSK-30 twin-screw extruderhad excellent cast film processability. Thin films were easily made fromthe pellets on the same Haake twin-screw film cast line used inExample 1. The barrel temperatures were set at 180, 190, 190 and 180° C.for zones 1, 2, 3 and 4 (die) respectively. The screw speed wasmaintained at 134 rpm. This film also crystallized very quickly. Highquality water-soluble film was again made using the temperature profileset forth in Example 2.

[0054] The tensile properties were tested under the same conditions asset forth in Example 2. It was found that the pellet-derived film wasslightly stronger than that powder-derived film The pellet-derived filmwas also slightly more rigid and slightly less ductile than thepowder-derived film.

[0055] The peak stress of the pellet-derived film is nearly twice thatof the powder-derived film, reaching a high value of 120 MPa versus a 60MPa for the powder-derived film The modulus of the pellet-derived filmwas about 30% higher than the powder-derived film, reaching 2580 MPa,while the powder film had a modulus of 1800 MPa. The powder-derived filmwas a little more ductile giving slightly higher elongation-at-break.Due to the peak stress and its contribution to the film's overalltensile toughness as measured as the area under the tensile curve, thepellet-derived PVOH film had a 50% higher toughness than thepowder-derived PVOH film.

[0056] PVOH film produced from the PVOH pellets was determined to bestronger and tougher than powder-derived PVOH film. Unexpectedly, itshowed an upgrade in tensile properties by subjecting the PVOH throughmore thermal processing. Typically, as a polymer is subjected to morethermomechanical stress, polymer degradation occurs which results in theloss of mechanical and other properties.

Examples 4-6

[0057] Next, three grades of PVOH from Air Products at fully and superhydrolyzed level, i.e. 98.8-−98.8% and +99.3% hydrolysis were selectedto determine whether they exhibited thermoplastic properties. Since allthree grades had a high degree of hydrolysis, the three resins wereselected based upon viscosity. The three grades were resins of low,medium and high viscosity. These grades ensured that the correlationbetween hydrolysis and molecular weight on thermoplastic processingcould be determined. Representing these three grades were Air ProductsAIRVOL® 107, 125, and 165 of respectively low, medium and high solutionviscosities (See Table 1). When these three grades of PVOH were extrudedon the Haake extruder used in Example 1, it was discovered that none ofthese grades could be extruded similar to that of Nippon KP-06. ThesePVOH resins caused the extruder to plug up. When the ZSK-30 extruderused in Example 3 was used, the same problems occurred. Therefore, PVOHfilms using PVOH having a high degree of hydrolysis could not beextruded, regardless of the viscosity of the resin.

Examples 7-17

[0058] Next, a broader comparison was done to determine the correlationof hydrolysis and viscosity of a particular PVOH resin versus thethermoplastic capability of the resin. In addition to the PVOH resinsused in Examples 1 and 4 to 6, four other grades of AIRVOL® resin wereused (AIRVOL® 203, 205, 523 and 540) along with three grades of DuPontELVANOL® resin (ELVANOL® 51-05, 52-22 and 50-42). The four AIRVOL® andthree ELVANOL® resins all are partially hydrolyzed (having a hydrolysisof between about 87 to about 90 percent), but varied viscosities. Table1 is a chart of solution viscosity versus percent hydrolysis accordingto vendor data, for the selected grades of PVOH. TABLE 1 Viscosity 4%solution, Manufacturer Trade Name % Hydrolysis 20° C. Nippon GohseiKP-06 71-74   5-7 Air Products AIRVOL ® 125 99.3+  26-30 AIRVOL ® 16599.3+  55-65 AIRVOL ® 107 98.0-98.8 5.4-6.5 AIRVOL ® 203 87.0-89.0   3-4AIRVOL ® 205 87.0-89.0   5-6 AIRVOL ® 523 87.00-89.0  22-26 AIRVOL ® 54087.0-89.0  40-50 DuPont ELVANOL ® 51-05 87.0-89.0   3-4 ELVANOL ® 52-2287.0-89.0  22-26 ELVANOL ® 50-42 87.0-89.0  40-50

[0059] Each of the above grades of PVOH were extruded on a Werner &Pfleiderer ZSK-30 twin-screw extruder in order to determine meltprocessability.

[0060] It was not obvious to tell which grades of PVOH would demonstratethermoplasticity from the percent hydrolysis and/or the solutionviscosity. Of the eleven resins studied, only four grades of PVOH weredetermined to have thermoplastic processability: NG KP-06, ELVANOL®51-05, AIRVOL® 205, and AIRVOL® 203. The melt strands of the KP-06strands were colorless, the AIRVOL® grades were slightly yellow colored,and the ELVANOL® grade was yellow. For each of the four resins, the meltstrands were transparent. The strands appeared very strong and brittle.

[0061] All of the other grades of PVOH were determined to not bethermoplastically processable. The extruded PVOH for thenon-thermoplastic grades was severely discolored, due to thermaldegradation. The strands had severe melt fracture, breakage, and/orbubble formation. After several minutes of extrusion, the degraded PVOHwould begin to plug the die holes and the percent torque and pressurewere observed to increase beyond the normal, safe operating range. ThePVOH would spit and/or pop out of the die or no material would extrudeat all, and the PVOH would begin to bridge at the feed throat. In somecases, the non-melt processable grades of PVOH would “freeze” and lockup the screws, triggering the extruder to shut off due to percent torqueoverload. The observed problems with extruding the non-thermoplasticgrades of PVOH made the observation of the melt processable,thermoplastic grades of PVOH even more remarkable.

[0062] Table 2 shows the average extrusion data for each of thethermoplastic grades of PVOH and two of the non-thermoplastic grades ofPVOH, ELVANOL® 52-22 and AIRVOL® 523, before the die holes were plugged.TABLE 2 Feed Screw BARREL TEMPERATURE Zone 7 Melt Die Rate Speed 1 2 3 45 6 Temp Temp Pres Trade Name (lb/hr) (rpm) % Torque (° C.) (° C.) (°C.) (° C.) (° C.) (° C.) (° C.) (° C.) (PSI) THERMOPLASTIC KP-06 20.00301 39.00 179 181 180 180 180 180 192 203 270 AIRVOL ® 205 20.04 30044.15 178 180 180 180 180 181 188 200 484 ELVANOL ® 51-05 19.79 30041.75 178 180 181 180 180 180 192 203 446 AIRVOL ® 203 20.02 299 42.78181 180 179 180 175 180 182 199 183 NON-THERMOPLASTIC AIRVOL ® 523 19.99300 54.95 178 180 179 182 181 181 199 213 1386 ELVANOL ® 52-22 20.01 30155.09 181 180 179 180 180 180 198 218 1511

[0063] As shown in Table 2, the melt processable, thermoplastic gradeshad lower percent torque (at least 20% lower), melt temperature (atleast 10° C. lower), and die pressure (over 65% lower), compared to thenon-thermoplastic grades. Thus, the qualitative observation of meltprocessability was confined by extrusion data.

[0064] Extruded pellets produced on the ZSK-30 extruder from each of thethermoplastic grades of PVOH were also converted into thin film on theHaake extruder, following the same procedure used for Example 3. NGKP-06 appeared to show the best film processability, in terms ofclarity, melt strength, and uniformity (with no visible gels). ELVANOL®51-05 produced a very thin film (down to less than 0.2 mil) withexcellent clarity. However, ELVANOL® 51-05 was not as “clean” as theKP-06 as shown by a few visible gels in the film AIRVOL® 203 and 205produced very thin films (drawn down to about 0.5 mil) with less claritythan NG KP-06 or ELVANOL® 51-05. The Air Products resins were even less“clean” with several gels in the film The gels in the film for AIRVOL®grades made it more difficult to draw down to less than 0.5 mil, becauseof splitting due to gels.

[0065] The non-thermoplastic grades of PVOH, in either powder orextruded pellet form, could not be converted into film on the Haakeextruder following the same procedure used for Example 3. No thin filmcould be produced for any of the non-melt processable grades. Severediscoloration and die pressure were observed. For some grades, totallyblack sheets of thick rigid plastic were produced. After severalminutes, the thin slit in the film die plugged and no thin film could becollected.

Examples 18-27

[0066] In addition to hydrolysis, the commercial grade PVOH resins weretested to determine whether or not the molecular weight of the PVOHcould be used to determine whether that particular resin was meltprocessable. The NG KP-06 resin, along with several of the AIRVOL® andELVANOL® resins were used. Gel permeation chromatography (GPC) results(obtained from American Polymer Standard Corporation, Mentor, Ohio) forthe number-average molecular weight (M_(n)), the weight-averagemolecular weight (M_(w)) and the Z-average molecular weight (M_(z)) ofthe PVOH resins, in either powder or pellet form, are shown in Table 3.TABLE 3 Polydisperity Trade Name Form M_(n) M_(w) M_(z) (M_(w)/M_(n))MELT PROCESSABLE KP-06 powder 5,150 8,750 12,800 1.71 AIRVOL ® 205powder 25,000 46,500 74,450 1.86 ELVANOL ® powder 22,350 45,850 75,9002.05 51-05 AIRVOL ® 203 powder 18,400 32,500 49,300 1.77 KP-06 pellets7,100 10,850 15,000 1.53 AIRVOL ® 205 pellets 30,750 52,400 85,700 1.70ELVANOL ® pellets 27,650 51,950 85,000 1.88 51-05 AIRVOL ® 203 pellets22,550 36,800 54,450 1.63 NOT MELT PROCESSABLE AIRVOL ® 523 pellets61,900 148,300 296,900 2.40 ELVANOL ® pellets 55,900 143,400 302,0002.57

[0067] The thermoplastic grades of PVOH powder had an average M_(w)ranging from 8,750 g/mole to 46,500 g/mole and M_(w)/M_(n) ranging from1.71 to 2.05. The same grades of PVOH, after extrusion and pelletizingon the ZSK-30 extruder, retained thermoplasticity and filmprocessability. The extruded pellets had an average M_(w) ranging from10,850 g/mole to 52,400 g/mole and M_(w)/M_(n) ranging from 1.63 to1.88. The non-thermoplastic grades of PVOH, however, had significantlyhigher M_(w) at 148,300 and 143,400 and higher M_(w)/M_(n) at 2.40 and2.57.

[0068] Interestingly, after twin-screw extrusion, the M_(w) of the meltprocessable grades of PVOH increased and the M_(w)/M_(n) decreased.Typically, after extrusion, a polymer would have been expected toundergo degradation, resulting in reduced M_(w) and increasedM_(w)/M_(n).

Examples 28-39

[0069] Finally, the commercial grade PVOH resins were tested todetermine whether or not the melt viscosity of the PVOH could be used todetermine whether that particular resin was melt processable. Again, theNG KP-06 resin, along with several of the AIRVOL® and ELVANOL® resinswere used. At a shear rate of 500 s⁻¹, the apparent melt viscosity ofthe thermoplastic and non-thermoplastic grades of PVOH weresignificantly different. Table 4 shows the apparent melt viscosity at ashear rate of 500 s⁻¹ for PVOH powder and pellets produced on the ZSK-30extruder. TABLE 4 Trade Name Form Melt Viscosity (Pa · s) MELTPROCESSABLE KP-06 powder 717 KP-06 pellets 686 ELVANOL ® 51-05 powder796 ELVANOL ® 51-05 pellets 1337 AIRVOL ® 203 powder 311 AIRVOL ® 203pellets 490 AIRVOL ® 205 powder 821 AIRVOL ® 205 pellets 1034 NOT MELTPROCESSABLE AIRVOL ® 523 powder 4010 ELVANOL ® 52-22 powder 1684ELVANOL ® 50-42 powder 2943 ELVANOL ® 52-22 pellets 2508

[0070] Unmodified PVOH with a melt viscosity greater than about 1500Pa·s was not melt processable and grades with a melt viscosity less than1500 Pa·s were melt processable.

[0071] As can be seen from the above examples, not all grades ofcommercially available PVOH resins are melt processable. In fact, onlyfour of the eleven grades tested exhibited thermoplasticcharacteristics. However, by using the hydrolysis, the molecular weight,the solution viscosity or the melt viscosity of the PVOH resins, it ispossible to determine which grades of PVOH are likely to be meltprocessable.

[0072] However, due to the current number and type of PVOH grades, it isdifficult to determine the exact ranges of melt processability for allpotential PVOH resins. For the current grades, it is possible todetermine the hydrolysis, the molecular weight and the solutionviscosity for those grades which definitely are melt-processable, andfor those grades which are not melt processable. However there is amiddle area for these parameters for which no grades of PVOH arecurrently available.

[0073] For example, while partially hydrolyzed PVOH resins (less than 90percent) and fully hydrolyzed resins (greater than 95 percent) areavailable, there are no commercially available resins in between (having90 to 95 percent hydrolysis). Therefore, it is difficult to determinethe exact ranges of melt processability for all unmodified PVOH resinsbased on the percent hydrolysis. Additionally, grades of PVOH having aweight-average molecular weight of less than 60,000 are meltprocessable, while grades having a weight-average molecular weightgreater than 140,000 are not melt processable. Therefore, it isdifficult to determine the exact ranges of melt processability for allunmodified PVOH resins based on the weight-average molecular weight.Finally, for solution viscosity, grades having a solution viscosity lessthan 10 cp are melt processable while grades having a solution viscositygreater than 20 cp are not, leaving the range from 10-20 cp uncertain.However, it is possible to determine the exact range of meltprocessability using melt viscosity. Those grades having a meltviscosity less than about 1500 Pa·s are melt processable while gradeshaving a melt viscosity greater than about 1500 Pa·s are not meltprocessable.

Example 40

[0074] A blend of 65% by weight of DuPont ELVANOL® 51-05 polyvinylalcohol resin powder and 35% by weight of a KRATON® thermoplasticelastomer, G-1659x (a tri-block copolymer of S-EB-S,polystyrene-co-ethylene-butylene-co-styrene with a glass transitiontemperature of the rubber block of −42° C.) was fed to acounter-rotating twin-screw extruder TW-100 (manufactured by Haake,Paramus, N.J.) at a rate of 5 pounds per hour (lb/hr). The extruder hada screw length of 300 mm. A 4″ die for film casting purpose(manufactured by Haake) was used to make cast film from the blend. Eachconical screw had a diameter of 30 mm at the feed port and a diamtere of20 mm at the die. The extruder had four heating zones which were set at170° C., 180° C., 180° C. and 175° C., respectively. The screw speed was70 rpm. The screw speed and the the film wind-up speed were adjusted toobtain a thin film of uniform thickness and substantially free from filmdefects. A translucent, soft film was formed.

[0075] The tensile tests of the films made from the blend of polyvinylalcohol and the thermoplastic elastomer were performed on a Sintech 1/Dtensile tester available from MTS Systems Corp., Machesny Park, Ill. Thefilm was cut into a type V dogbone shape in accordance with ASTM D638.The test was performed with a grip separation of 30 mm and a crossheadspeed of 4 mm/second.

[0076] The resulting tensile properties of the PVOH/KRATON® blend filmsare shown in Table 5. TABLE 5 65/35 PVOH/KRATON ® PVOH control filmblend film Film thickness (mil) 1.0 1.3 Peak Stress (MPa) 63 45Strain-at-Break (%) 74 83 Modulus (MPa) 1476 896

[0077] As shown by the data in the table, the strain-at-break increasedfrom 74% to 83% and the tensile modulus decreased from 1476 to 896 MPa,thereby showing improved ductility and softness.

[0078] Therefore, these results have shown that blends includingunmodified PVOH and a thermoplastic elastomer may be used in the absenceof any chemical modification or grafting of the PVOH, or without theaddition of any plasticizing agent or water to produce qualitythermoplastic film and fibers comprising a blend of the PVOH and thethermoplastic elastomer. The use of an unmodified PVOH in these blendsavoids the additional process steps associated with chemicalmodification or grafting of the PVOH and the problems associated withthe use of plasticizers with the PVOH.

We claim:
 1. A substantially water-free thermoplastic article comprisingfrom about 1 to about 99% by weight of an unmodified polyvinyl alcoholand from about 99 to about 1% by weight of a thermoplastic elastomer. 2.The thermoplastic article of claim 1, wherein a 4% in water solution ofthe unmodified polyvinyl alcohol at 20° C. has a viscosity of less thanabout 20 centipoise.
 3. The thermoplastic article of claim 2, wherein a4% in water solution of the unmodified polyvinyl alcohol at 20° C. has aviscosity of less than about 10 centipoise.
 4. The thermoplastic articleof claim 1, wherein the unmodified polyvinyl alcohol has a hydrolysis ofless than about 95%.
 5. The thermoplastic article of claim 4, whereinthe unmodified polyvinyl alcohol has a hydrolysis of less than about90%.
 6. The thermoplastic article of claim 1, wherein the unmodifiedpolyvinyl alcohol has a weight-average molecular weight of less thanabout 140,000.
 7. The thermoplastic article of claim 6, wherein theunmodified polyvinyl alcohol has a weight-average molecular weight ofless than about 60,000.
 8. The thermoplastic article of claim 1, whereinthe unmodified polyvinyl alcohol has a melt viscosity at a shear rate of500 s⁻¹ of less than about 1500 Pa·s.
 9. The thermoplastic article ofclaim 1, wherein the thermoplastic article has less than about 2.0percent by weight of water.
 10. The thermoplastic article of claim 1,wherein the thermoplastic article has less than about 1.0 percent byweight of water.
 11. The thermoplastic article of claim 1, wherein thethermoplastic article has less than about 0.5 percent by weight ofwater.
 12. The thermoplastic article of claim 1, wherein thethermoplastic elastomer is selected frompolystyrene-polybutadiene-polystyrene block polymer,polystyrene-polyisoprene-polystyrene block polymer,polystyrene-poly(ethylene-butylene)-polystyrene block polymer,polystyrene-poly(ethylene-propylene)-polystyrene block polymer,elastomeric polyurethanes, ethylene-octene copolymers, polyesterpolyurethane, natural rubber, nitrile rubber, butyl rubber,ethylene-propylene terpolymers, silicone rubber, polyurethane rubber,thermoplastic rubbers, elastomeric block copolymers, copolymers ofpolyethylene oxide and polybutylene terephthalate, polyamide-polyetherblock copolymers, styrenic block copolymers, elastomeric polypropylene,or mixtures thereof.
 13. The thermoplastic article of claim 1, whereinthe thermoplastic article comprises from about 50 to about 90% by weightof an unmodified polyvinyl alcohol and from about 50 to about 10% byweight of a thermoplastic elastomer.
 14. The thermoplastic article ofclaim 1, wherein the thermoplastic article comprises from about 65 toabout 80% by weight of an unmodified polyvinyl alcohol and from about 35to about 20% by weight of a thermoplastic elastomer.
 15. Thethermoplastic article of claim 1, wherein the thermoplastic article is afilm.
 16. The thermoplastic article of claim 1, wherein thethermoplastic article is a fiber.
 17. A thermoplastic article comprisingfrom about 1 to about 99% by weight of an unmodified polyvinyl alcoholand from about 99 to about 1% by weight of a thermoplastic elastomer,wherein the thermoplastic article has less than about 2.0 percent byweight of water.
 18. The thermoplastic article of claim 17, wherein a 4%in water solution of the unmodified polyvinyl alcohol at 20° C. has aviscosity of less than about 20 centipoise.
 19. The thermoplasticarticle of claim 18, wherein a 4% in water solution of the unmodifiedpolyvinyl alcohol at 20° C. has a viscosity of less than about 10centipoise.
 20. The thermoplastic article of claim 17, wherein theunmodified polyvinyl alcohol has a hydrolysis of less than about 95%.21. The thermoplastic article of claim 20, wherein the unmodifiedpolyvinyl alcohol has a hydrolysis of less than about 90%.
 22. Thethermoplastic article of claim 17, wherein the unmodified polyvinylalcohol has a weight-average molecular weight of less than about140,000.
 23. The thermoplastic article of claim 22, wherein theunmodified polyvinyl alcohol has a weight-average molecular weight ofless than about 60,000.
 24. The thermoplastic article of claim 17,wherein the unmodified polyvinyl alcohol has a melt viscosity at a shearrate of 500 s⁻¹ of less than about 1500 Pa·s.
 25. The thermoplasticarticle of claim 17, wherein the thermoplastic elastomer is selectedfrom polystyrene-polybutadiene-polystyrene block polymer,polystyrene-polyisoprene-polystyrene block polymer,polystyrene-poly(ethylene-butylene)-polystyrene block polymer,polystyrene-poly(ethylene-propylene)-polystyrene block polymer,elastomeric polyurethanes, ethylene-octene copolymers, polyesterpolyurethane, natural rubber, nitrile rubber, butyl rubber,ethylene-propylene terpolymers, silicone rubber, polyurethane rubber,thermoplastic rubbers, elastomeric block copolymers, copolymers ofpolyethylene oxide and polybutylene terephthalate, polyamide-polyetherblock copolymers, styrenic block copolymers, elastomeric polypropylene,or mixtures thereof.
 26. The thermoplastic article of claim 17, whereinthe thermoplastic article comprises from about 50 to about 90% by weightof an unmodified polyvinyl alcohol and from about 50 to about 10% byweight of a thermoplastic elastomer.
 27. The thermoplastic article ofclaim 17, wherein the thermoplastic article comprises from about 65 toabout 80% by weight of an unmodified polyvinyl alcohol and from about 35to about 20% by weight of a thermoplastic elastomer.
 28. Thethermoplastic article of claim 17, wherein the thermoplastic article isa film.
 29. The thermoplastic article of claim 17, wherein thethermoplastic article is a fiber.
 30. A substantially water-free blendcomposition comprising from about 1 to about 99% by weight of anunmodified polyvinyl alcohol and from about 99 to about 1% by weight ofa thermoplastic elastomer.
 31. A personal care article comprising thecomposition of claim
 1. 32. The personal care article of claim 31,wherein the personal care article is a diaper.
 33. The personal carearticle of claim 31, wherein the personal care article is a femininepad.
 34. The personal care article of claim 31, wherein the personalcare article are training pants.
 35. The personal care article of claim31, wherein the personal care article is an adult incontinence product.